The present invention is directed to an assembling device for web-like workpieces consisting of superposed and glued layers. The device is used as a double-facer of a machine producing corrugated board and on which the layers continuously run in the form of a web.
For an appropriate presentation the invention will be described particularly in relation with a so-called double-facer.
As a rule, corrugated board is composed of a first so-called single-faced board layer consisting of fluted paper glued on a flat liner paper. This first layer is then assembled also by gluing with a second layer, which second layer may be either a second flat outer liner paper so as to form a so-called double-faced corrugated board or the second layer may be a second single-faced board to which an added outer liner paper is also applied so as to form a so-called double wall corrugated board. Corrugated boards with triple fluting is also produced in a similar way. A machine, which produces the corrugated board and is also called a corrugator, usually comprises a first so-called wet end in which the board is actually made and a second so-called dry end in which the web-like board is cut into individual sheets which are then piled up.
The first so-called wet end begins with a station, which is generally called a single-facer in the industry. In this station, the paper to be fluted after previously heating up and moistening runs through between two corrugating rolls themselves heated with steam. The flutes are shaped and held against the lower corrugating roll due to the action of either fingers or with regard to the cylinder outer means with which provides an overpressure or inner means in which a low pressure or vacuum is applied. An adjacent gluing drum applies glue on the tips of the flutes and then a preheated liner sheet is applied under pressure and with heat input against the tips by a pressing drum which is adjacent to the gluing drum and which pressing drum is also heated with steam. The glue will them immediately adhere owing to the effect of pressure and heat input.
The single-face corrugated board which is thus shaped then runs into a so-called glue unit which applies glue on the outer tips of the flutes which are still exposed. About one third of the water content in the glue amalgamates with the solid matter to form an adhesive whereas the remaining two thirds is freely available water which increases the paper moisture at this stage.
The single-face board thus provided with glue then runs on into a so-called double facer where it is joined with a second liner paper or else with the second single-faced intermediary board itself which is joined with a liner. The purpose of this double-facer is thus to put and hold together the various layers by simultaneously providing the necessary heat for the gelling of the glue and the removal of the moisture, to carry the amalgamated board forward, while continuing the elimination of moisture, and to hold the board flat throughout the cool-down process.
Considering the presence of the flutes, it is easy to understand that it is not possible to apply high pressure in the double-facer between the board layers, which is different than the prior action in the single-facer. This pressure reduction requires less heat input and thus much more time to get the glue gelled. In other words, at this stage of manufacture, the board travels continuously in the form of a web and the longer setting time will require an increase in the length of the double-facer.
The double-facer consists generally of a heating section as well as a pulling or second section onto also called a cooling section.
In the heating or first section the various layers destined to make up the corrugated board are applied on a number of heating plates with the help of an upper belt traveling through the whole station. An application pressure is exerted by the pressure roller acting on the upper belt. Another way of subjecting the various layers to pressure consist in using blowing cases or plenums which are arranged above the lower path of the upper belt and exert a uniform pressure on the whole upper side of the belt and, thus, on the various layers of the corrugated board. As a rule, the first section has 18 to 24 heating plates arranged in three or four sub-assemblies with each plate which extends perpendicular to the travel line of the corrugated board being produced. The plates have a lengthwise dimension slightly greater than the usable width of the corrugator and thus a width of about 50 cm. The plates are steam heated for each assembly.
A subsequent pulling section includes a lower drive belt which is driven synchronously with the upper belt. The corrugated boards are held between the two belts in order to be pulled out by the friction from the heating section.
The major draw back of such a double-facer is its considerable length. In fact, the production speed wanted determines not only the number of heating places required for the heat transfer into the corrugated board in order to cause the glue to gel and the water surplus contained in the corrugated board to be removed but also the length of the pulling section on account of the frictional forces involved. Similarly, the mechanical power required for the drive of the belt also becomes very significant. In addition, impurities, which are accumulating gradually in the joining areas between the plates, can reach such a point that they will scratch the lower liner of the corrugated board. This is all the more undesirable if the liner has undergone an embellishment treatment such as a coating or printing.
Finally, if it appears appropriate to use blowing cases or plenums in the heating section, the upper belt should almost certainly consist of a felt in order to insure sufficient friction between the upper belt and the corrugated web. In fact, a mesh belt has the advantage of letting water-laden air through the belt to provide uniformly applied pressures on the corrugated web; however, it does not build up any force of adherence between the belt and the corrugated board that would be sufficient for ensuring traction. However, such a force of adhesion or traction is generally useful for pulling the corrugated board through the device. On conventional devices, the considerable length of the successive heating plates entails a friction-type braking force to such an amount that all forces of adherence or traction appearing between the upper and lower belts and between the upper belt and the corrugated board will be necessary for transportation. A decease of the force of adherence between the upper belt and the corrugated board in the area of the blowing cases, which decrease would result from the use of a mesh belt, is thus inadmissable. On the other hand, the felt belt has the serious drawback of gathering moisture instead of letting it pass. So if so-called heavy corrugated boards are to be produced, the accumulation of moisture is likely to jeopardize production speed.
U.S. Pat. No. 3,217,425, a double-facer is proposed as an assembling device which does not use heating plates but comprises a lower belt acting together with supporting rollers and an upper belt running under the pressure rollers as well as under the upper nozzles, which are blowing hot air onto the corrugated board being produced. The air is immediately sucked into the lower pressure case. However, considering the excessive heating and drying performance of the device, the corrugated board has a tendency to warp quickly at the outlet depending on the excessive and insufficient moisture of the single-face board and/or of the various layers at the inlet. It is, thus, foreseen to put into operation a complex device for measuring the amount of warping at the outlet and providing a control for the preheating means, which act individually on each layer at the inlet. Nonetheless, the stabilization of this loop due to the counter-reaction is rather difficult to achieve and includes the secondary risk of overheating the glue prior to the layers being assembled.